Dump vehicle overturn preventing device

ABSTRACT

Provided is an overturn preventing device for a dump vehicle equipped with a body ( 3 ) and hoist cylinders ( 5 ). The dump vehicle overturn preventing device comprises: a loaded weight estimation unit ( 32 ) which estimates loaded weight on the body; a vehicle rotation moment calculation unit ( 33 ) which calculates a vehicle rotation moment Mb caused by movement of the dump vehicle&#39;s load upon discharging of the load; a reference moment calculation unit ( 34 ) which determines a reference moment Ms not greater than an overturn threshold moment MI which is the minimum value of a rotation moment required to lift the front wheels ( 1 ) off the ground; a judgment unit ( 35 ) which judges whether or not the vehicle rotation moment Mb has exceeded the reference moment Ms; and a display device ( 37 ) which notifies the driver that there is a probability of an overturn of the vehicle when the vehicle rotation moment Mb is judged to have exceeded the reference moment Ms. The device thus prevents overturning of the vehicle caused by the load sliding down from the body in a lump.

TECHNICAL FIELD

The present invention relates to a dump vehicle overturn preventingdevice for preventing a dump vehicle from overturning when the load isdischarged from the dump vehicle by tilting its body.

BACKGROUND ART

Dump vehicles, for carrying a load (object of transportation) such asexcavated earth and sand to a dumping site and discharging the load bytilting the body, are used at quarries, mines, etc. When a dump vehicleis parked on irregular ground or sloping ground, the dump vehicle mayfall into an unstable state due to tilting of the vehicle itself,fragility of the ground, etc. As its body is tilted to discharge theload in such a state, the barycenter of the entire vehicle rises due tothe tilting of the body which causes the vehicle to become unstable andpossibly overturn. There has been known a technique for preventing theoverturn upon discharging of a load, in which the tilt angle of thevehicle is monitored using measurement means such as an angle meter andthe tilting action of the body is restricted when the tilt angle hasincreased to a prescribed angle or more (see Patent Document 1).

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP,A 2002-307996

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

When a dump vehicle discharges its load by tilting the body, theearth/sand (load) generally collapses gradually from its lower part withthe increase in the tilt angle of the body and the collapsed earth/sandslides down along the tilted body to be discharged. However, in caseswhere the load adheres to the body due to reasons such as high viscosityof the load, the entire load may slide down in a lump as the tilt angleof the body exceeds a certain angle. This may break the dynamic balanceof the chassis and cause the vehicle to overturn. Thus, intending toprevent overturning of a vehicle by just monitoring the static balance(tilt angle of the vehicle) as in the technique of the aforementionedPatent Document 1 is not necessarily sufficient in some cases.

The object of the present invention, which has been made inconsideration of the above problem, is to provide a dump vehicleoverturn preventing device for preventing overturning of a vehiclecaused by its load sliding down from its body in a lump.

Means for Solving the Problem

To achieve the above object, the present invention provides an overturnpreventing device for a dump vehicle equipped with a body rotatablysupported on a frame and hoist cylinders that expand and contract torotate the body around its rotation axis, the device comprising: loadedweight estimation means which estimates loaded weight on the body;vehicle rotation moment calculation means which calculates a vehiclerotation moment caused by movement of the dump vehicle's load upondischarging of the load based on the loaded weight estimated by theloaded weight estimation means; reference moment calculation means whichcalculates the minimum value of the rotation moment required to lift thefront wheels of the vehicle off the ground and sets a reference momentnot greater than the minimum value; judgment means which judges whetheror not the vehicle rotation moment calculated by the vehicle rotationmoment calculation means has exceeded the reference moment calculated bythe reference moment calculation means; and notification means whichnotifies the driver that there is a probability of an overturn of thevehicle when the judgment means judges that the vehicle rotation momenthas exceeded the reference moment.

Effect of the Invention

The present invention prevents overturning of a vehicle caused by itsload sliding down from its body in a lump.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall schematic diagram of a dump vehicle in accordancewith an embodiment of the present invention.

FIG. 2 is an overall block diagram of a dump vehicle overturn preventingdevice in accordance with a first embodiment of the present invention.

FIG. 3 is a side view showing the dump vehicle in accordance with thefirst embodiment of the present invention when the dump vehicle isdischarging the load.

FIG. 4 is a flow chart showing the flow of a process for judging theprobability of an overturn of the vehicle which is executed by the dumpvehicle overturn preventing device in accordance with the firstembodiment of the present invention.

FIG. 5 is a side view of a dump vehicle in accordance with a secondembodiment of the present invention when the dump vehicle is dischargingthe load.

FIG. 6 is an overall block diagram of a dump vehicle overturn preventingdevice in accordance with the second embodiment of the presentinvention.

FIG. 7 is a schematic diagram showing the idea of road shoulder strengthcalculation employed in the second embodiment of the present invention.

FIG. 8 is a flow chart showing the flow of a process for judging theprobability an overturn of the vehicle which is executed by the dumpvehicle overturn preventing device in accordance with the secondembodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Referring to the drawings, a description will be given in details ofpreferred embodiments in accordance with the present invention.

FIG. 1 is an overall schematic diagram of a dump vehicle in accordancewith an embodiment of the present invention. FIG. 2 is an overall blockdiagram of a dump vehicle overturn preventing device in accordance witha first embodiment of the present invention.

The dump vehicle shown in the figure mainly comprises front wheels 1 andrear wheels 2 each attached to the front and rear part of a frame 4, abody 3 rotatably supported on the frame 4 via a support shaft 6, hoistcylinders 5 that expand and contract to rotate the body 3 around thesupport shaft 6, a main control device 40 of the dump vehicle overturnpreventing device, and a display device (notification means) 37installed in the cab.

The front wheels 1 are equipped with a front axle load sensor (frontaxle load detecting means) 31A for detecting the total load acting onthe front wheels 1. The rear wheels 2 are equipped with a rear axle loadsensor (rear axle load detecting means) 31B for detecting the total loadacting on the rear wheels 2. In other words, the front axle load sensor31A detects the load acting on the front of the vehicle and the rearaxle load sensor 31B detects the load acting on the rear of the vehicle.These sensors 31A and 31B may be configured by force sensors attached tosuspension mechanisms for the front and rear wheels 1 and 2, forexample. In cases where the suspension mechanisms for the front and rearwheels 1 and 2 are configured with hydraulic mechanisms, for example,the loads acting on the front and rear wheels 1 and 2 can be detectedwith ease by measuring pressures inside hydraulic cylinders supportingthe suspension mechanisms for the front and rear wheels 1 and 2,respectively.

Main components such as the drive system and the cab seat are mounted onthe frame 4. The vehicle is capable of freely traveling on the roadsurface with the front and rear wheels 1 and 2. When the hoist cylinders5 are expanded, the front end of the body 3 raises and the tilt angleincreases while the body 3 rotates around the support shaft 6. With thismovement, the load 7 (object of transportation) loaded on the body 3 canbe discharged from the rear end of the body 3. The support shaft 6 isequipped with a potentiometer (rotary potentiometer) 38 for measuringthe rotation angle of the support shaft 6, as angle detecting means fordetecting the tilt angle of the body 3 with respect to the frame 4.

In the dump vehicle overturn preventing device shown in FIG. 2, the maincontrol device 40 includes a loaded weight estimation unit (loadedweight estimation means) 32, a vehicle rotation moment calculation unit(vehicle rotation moment calculation means) 33, a reference momentcalculation unit (reference moment calculation means) 34, a judgmentunit (judgment means) 35 and a cylinder controller (cylinder controlmeans) 39.

The loaded weight estimation unit 32 is connected with the front axleload sensor 31A and the rear axle load sensor 31B. The loaded weightestimation unit 32 estimates the weight “m” of the load 7 (loadedweight) by subtracting the empty weight of the dump vehicle from the sumtotal of load data (detected values) acquired from the front axle loadsensor 31A and the rear axle load sensor 31B.

The reference moment calculation unit 34 is connected with the frontaxle load sensor 31A and the rear axle load sensor 31B. The referencemoment calculation unit 34 calculates an overturn threshold moment MI(explained later) based on the load data acquired from the front axleload sensor 31A and the rear axle load sensor 31B and then sets areference moment Ms not greater than the calculated overturn thresholdmoment MI.

Here, the overturn threshold moment MI represents the vehicle rotationmoment of when the load on the front wheels 1 falls below 0, that is,the minimum value of a rotation moment around the rear wheels 2(fulcrum) required to lift the front wheels 1 off the ground. Theoverturn threshold moment MI is acquired by calculating the barycentricposition of the vehicle from the load data acquired from the front axleload sensor 31A and the rear axle load sensor 31B. The reference momentMs is used as the reference for judging whether or not to notify thedriver via the display device 37 that there is a strong probability ofthe vehicle to overturn. The reference moment Ms is set at a value notgreater than the overturn threshold moment MI. While it is possible todirectly use the calculated overturn threshold moment MI as thereference moment Ms, overturning of the vehicle can be prevented withhigher reliability as smaller the reference moment Ms is set than theoverturn threshold moment MI.

An example of a method for calculating the overturn threshold moment MIwill be explained. Let “Lw” represent the distance between the frontwheels 1 and the rear wheels 2 of the dump vehicle (i.e., thewheelbase), “Ff” represent wheel reaction force determined based on theload data acquired from the front axle load sensor 31A, “Fr” representwheel reaction force determined based on the load data acquired from therear axle load sensor 31B, and “F” represent the total load (F=Ff+Fr).The distance Lr from the rear wheels 2 to the barycenter is representedby the following expression (1).Lr=Lw×(Ff/F)  (1)Meanwhile, the overturn threshold moment MI required to lift the totalload F around the rear wheels 2 is represented by the followingexpression (2).MI=Lr×F  (2)Thus, by substituting the expression (1) into the expression (2), theoverturn threshold moment MI can be represented by the followingexpression (3).MI=Lw×Ff  (3)

The vehicle rotation moment calculation unit 33 is connected with theloaded weight estimation unit 32. The vehicle rotation momentcalculation unit 33 calculates a vehicle rotation moment caused bymovement of the load 7 upon its discharging based on the loaded weightestimated by the loaded weight estimation unit 32. The vehicle rotationmoment is the moment exerted when the body 3 rotates around the supportshaft 6 to discharge the load 7 (object of transportation). The vehiclerotation moment takes a high value when the load 7 slides down from thebody 3 in a lump. The vehicle rotation moment calculation unit 33 inthis embodiment calculates a vehicle rotation moment that is expected tooccur when the load 7 slides down from the body 3 in a lump.

Next, an example of a method for calculating the vehicle rotation momentwill be explained below referring to FIG. 3.

FIG. 3 is a side view showing the dump vehicle in accordance with thefirst embodiment of the present invention where the vehicle isdischarging the load 7. In this figure, when the load 7 moves to therear part of the body 3 in a lump, the body 3, which is rotatable aroundthe support shaft 6 as the fulcrum, receives a rotation moment(clockwise in FIG. 3) due to the weight of the load 7. Let “m” representthe loaded weight estimated by the loaded weight estimation unit 32, “g”represent the gravitational acceleration, and “θ” represent the tiltangle of the body 3 with respect to the horizontal plane. The rear endof the body 3 receives a load up to a maximum of m×g×cos θ on theassumption that the load 7 slides down in a lump upon discharging. Thus,let “Lb” represent the distance from the support shaft 6 to the rear endof the body 3, the vehicle rotation moment Mb occurring when the load 7slides down from the body 3 in a lump can be represented by thefollowing expression (4).Mb=Lb×m×g×cos θ  (4)Incidentally, the tilt angle θ of the body 3 with respect to thehorizontal plane can be acquired by using an angle sensor that detectsthe tilt angle of the body 3 with respect to the horizontal plane, or byadding up detected values of the potentiometer 38 and an angle sensorthat detects the tilt angle of the frame 4 with respect to thehorizontal plane, for example.

Returning to FIG. 2, the judgment unit 35 is connected with the vehiclerotation moment calculation unit 33 and the reference moment calculationunit 34. The judgment unit 35 judges whether the vehicle rotation momentMb exceeds the reference moment Ms or not based on the values of themoments Mb and Ms inputted from the vehicle rotation moment calculationunit 33 and the reference moment calculation unit 34. In the case wherethe reference moment calculation unit 34 sets the reference moment Ms ata value equal to the overturn threshold moment MI, the judgment unit 35uses the following expression (5) derived from the above expressions (3)and (4) to judge the probability of the vehicle to overturn.Lb×m×g×cos θ>Lw×Ff  (5)

When the judgment unit 35 judges that the expression (5) holds, there isa strong probability that the front wheels 1 lift and the state of thevehicle turns unstable since the front/rear weight distribution of thevehicle shifts to the rear of the vehicle when the load 7 is dischargedin a lump. In this case, the judgment unit 35 transmits a signal formaking the display device 37 display information indicating that thereis a strong probability of the vehicle to overturn. The judgment unit 35may also be configured to transmit a signal for reducing the expansionspeed of the hoist cylinders 5 or for stopping the expansion of thehoist cylinders 5 to the cylinder controller 39, in addition to or inplace of the signal transmitted to the display device 37.

The display device 37 (e.g., high-definition LCD (Liquid CrystalDisplay) monitor) is connected with the judgment unit 35. The displaydevice 37 is set at a position in the cab easily viewable to the driver.When the judgment unit 35 judges that the vehicle rotation moment Mb hasexceeded the reference moment Ms, information (characters, figures,signs, combination thereof, etc.) indicating that there is a strongprobability of an overturn of the vehicle is displayed on the displaydevice 37. The notification by the display device 37 indicating a strongprobability of the vehicle to overturn allows the driver to recognizethat there is a possibility of the vehicle to overturn. Incidentally,while the display device 37 is taken as an example of the means fornotifying the driver of a strong probability of an overturn of thevehicle (notification means) in this embodiment, the notification mayalso be made by providing a warning lamp arranged in the meter panel ofthe cab, a device such as a buzzer that makes a warning sound, etc.

The cylinder controller 39 is connected with the judgment unit 35. Thecylinder controller 39 reduces the expansion speed of the hoistcylinders 5 or stops the expansion of the hoist cylinders 5 when thejudgment unit 35 judges that the vehicle rotation moment Mb has exceededthe reference moment Ms. As a guideline, the expansion speed of thehoist cylinders 5 after the control by the cylinder controller 39 may beset at a speed that is lower than a speed at which the load 7 is notdischarged in a lump.

A switch 36 connecting/disconnecting the judgment unit 35 to/from thedisplay device 37 and the cylinder controller 39 may also be provided asshown in FIG. 2. The switch 36, which is connected with an anglejudgment unit 11, is properly opened and closed depending on the tiltangle of the body 3 detected by the potentiometer 38.

The angle judgment unit 11, which is connected with the potentiometer38, judges whether or not the tilt angle detected by the potentiometer38 has exceeded a preset angle. The preset angle is an angle (angularvalue) stored in the angle judgment unit 11 (or in a storage unit(unshown) of the main control device 40, etc.). The preset anglerepresents a tilt angle of the body 3 at which a vehicle rotation momentso strong as to overturn the vehicle will not occur. For example, whenthe preset angle is set at an angle such that a load having lowviscosity (e.g., earth and sand) would naturally crumble down and bedischarged from the body 3 as the body 3 is tilted to that angle, theload on the body 3 can be presumed to have high viscosity if the loadremains on the body 3 even when the body 3 is tilted over the presetangle. In this case, it is clear that there is a strong probability ofthe load sliding down in a lump and it is highly necessary to considerthe risk of the overturning of the vehicle.

The angle judgment unit 11 is configured to close the switch 36 when thetilt angle detected by the potentiometer 38 is judged to exceed thepreset angle and to open the switch 36 otherwise. With thisconfiguration, the displaying of the information indicating a strongprobability of the vehicle to overturn on the display device 37 and thespeed control of the hoist cylinders 5 by the cylinder controller 39 arecarried out only when the value (angle) detected by the potentiometer 38is greater than the preset angle.

Next, the operation of the dump vehicle overturn preventing deviceconfigured as above will be described below. FIG. 4 is a flow chartshowing the flow of a process for judging the probability of overturningof the vehicle which is executed by the dump vehicle overturn preventingdevice in accordance with the first embodiment of the present invention.

The process shown in FIG. 4 is started when a switch (unshown) fortilting the body 3 is operated to discharge the load 7. First, the maincontrol device 40 inputs the load data acquired by the axle load sensors31A and 31B (sensor values) to the loaded weight estimation unit 32 andthe reference moment calculation unit 34 (step 61). Subsequently, theloaded weight estimation unit 32 estimates the loaded weight “m” fromthe load data acquired by the axle load sensors 31A and 31B (step 62).The vehicle rotation moment calculation unit 33 calculates the vehiclerotation moment Mb using the loaded weight “m” estimated by the loadedweight estimation unit 32 (step 63).

Meanwhile, the reference moment calculation unit 34 calculates thebarycentric position of the vehicle from the load data of the axle loadsensors 31A and 31B acquired in the step 61, calculates the overturnthreshold moment MI using the barycentric position, and sets thereference moment Ms based on the overturn threshold moment MI (step 64).

After the step 64 is finished, the judgment unit 35 compares the vehiclerotation moment Mb calculated in the step 63 with the reference momentMs calculated in the step 64 (step 65). If the vehicle rotation momentMb is equal to or lower than the reference moment Ms, the processreturns to the step 61 and the subsequent steps are repeated. Incontrast, if the vehicle rotation moment Mb is greater than thereference moment Ms in the step 65, the information indicating a strongprobability of an overturn of the vehicle is displayed on display device37 for the driver (step 66). Thereafter, the process from the step 61 isrepeated. As above, according to this embodiment, it is possible topresent information that can prompt the driver to make a rationalsituational judgment in regard to the risk of an overturn of thevehicle.

As described above, in the dump vehicle overturn preventing device inaccordance with the present invention, when the load (object oftransportation) 7 (e.g., earth and sand) is discharged by tilting thebody 3, the reference moment Ms is set by calculating the overturnthreshold moment MI, which is the moment at the instant the vehicle isto overturn (i.e., at the instant the vertical load on the front wheels1 falls below 0 due to the movement of the barycentric position), fromthe barycentric position determined from the load distribution measuredby the axle load sensors 31A and 31B and already-known positional dataof the wheels 1 and 2. Further, the vehicle rotation moment Mb aroundthe support shaft 6 caused by the movement of the load upon itsdischarging is calculated from the loaded weight “m” estimated by theloaded weight estimation unit 32, already-known shape data of the body 3and already-known positional data of the body support shaft 6. Then, themagnitude relationship between the vehicle rotation moment Mb and thereference moment Ms is judged. With this operation, information on thedanger of overturning of the vehicle, considering not only the staticbalance (overturn caused by the lifting of either the front wheels 1 orthe rear wheels 2 due to the movement of the barycentric position) butalso the dynamic balance (overturn caused by the lifting of the frontwheels 1 due to the rotation moment caused by the movement of the loadupon its discharging), can be presented to the driver via the displaydevice 37. The driver notified of the danger of the vehicle overturn viathe display device 37 can take countermeasures such as reducing theexpansion speed of the hoist cylinders 5 or stopping the expansion ofthe hoist cylinders 5, whereby overturning of the vehicle caused by theload 7 sliding down from the body 3 in a lump can be prevented.

Here, effects of the open/close control of the switch 36 in the aboveembodiment (conducted by the angle judgment unit 11 depending on thetilt angle of the body 3) will be explained. In this control, the switch36 is closed only when the angle judgment unit 11 judges that the tiltangle of the body 3 has exceeded the preset angle. Therefore, thewarning that there is a strong probability of a vehicle overturn isdisplayed on the display device 37 only when the tilt angle of the body3 is greater than the preset angle and the vehicle rotation moment Mb isgreater than the reference moment Ms. Thus, when the tilt angle of thebody 3 is small, the notification of the warning is stopped since theprobability of occurrence of a great vehicle rotation moment Mb is low.When the tilt angle of the body 3 is large and the load 7 remains on thebody 3, the warning is issued since the probability of occurrence of agreat vehicle rotation moment Mb (caused by the sliding down of the load7 in a lump) exceeding the reference moment Ms (overturn thresholdmoment MI) is high. As a result, unnecessary issuance of warnings can bereduced and the driver can receive a warning only when it is highlynecessary.

In addition, effects of the control of the expansion speed of the hoistcylinders 5 in the above embodiment. (conducted by the cylindercontroller 39 depending on the vehicle rotation moment Mb) will beexplained below. In this control, the reduction of the tilting speed ofthe body 3 or the stoppage of the tilting of the body 3 can be conductedautomatically in response to the judgment by the judgment unit 35 thatthe probability of the vehicle to overturn is high. Thus, it becomespossible to automatically stabilize the chassis when the probability ofoccurrence of a great vehicle rotation moment Mb (due to the slidingdown of the load 7 in a lump) gets high. As a result, overturning of thevehicle can be prevented with high reliability.

Next, a second embodiment of the present invention will be described indetails. FIG. 5 is a side view of a dump vehicle in accordance with thesecond embodiment of the present invention when the dump vehicle isdischarging the load. In FIG. 5, elements identical with those in theforegoing figures are assigned the same reference characters andrepeated explanations thereof are omitted for brevity (ditto forsubsequent figures).

In FIG. 5, the shoulder of the road has a road surface part 20 and aslope face part 21 formed to have a falling gradient with respect to theroad surface part 20. The dump vehicle is parked on the road surfacepart 20, with its rear (load discharging part of the vehicle) facing theslope face part 21. The dump vehicle is equipped with a road shouldershape sensor (road shoulder shape measurement means) 8.

The road shoulder shape sensor 8 is a sensor for measuring the distancefrom the vehicle to the slope face part 21 behind the vehicle and theshape of the road shoulder. The road shoulder shape sensor 8 is attachedto the rear part of the dump vehicle. More specifically, the roadshoulder shape sensor 8 in this embodiment measures the distance fromthe ground contacting position of the rear wheels 2 (where the rearwheels 2 contact the ground) to the slope face part 21 and the shape ofthe road shoulder (road surface part 20, slope face part 21) andconverts the measured distance and shape into data. In the followingexplanation, the data regarding the distance and the shape may bereferred to as “road shoulder shape data”. The road shoulder shape datameasured by the road shoulder shape sensor 8 is outputted to a roadshoulder strength calculation unit 54 (explained later) of a maincontrol device 40A.

Incidentally, the road shoulder shape sensor 8 may be a laser radar,etc. The laser radar optically measures the distance from the sensor 8to the road shoulder with for instance an infrared laser beam andacquires the road shoulder shape data based on a sequence of pointsobtained by the measurement. The road shoulder shape sensor 8 may alsobe a distance detecting device that uses a millimeter wave array or anultrasonic array, an image recognition device that extracts distanceinformation by processing images shot by an image pickup device(camera), etc. It is desirable that the road shoulder shape sensor 8 isset at a position as high as possible at the rear of the vehicle inorder to facilitate the measurement of the shapes of the road surfacepart 20 and the slope face part 21.

FIG. 6 is an overall block diagram of a dump vehicle overturn preventingdevice in accordance with the second embodiment of the presentinvention. The overturn preventing device shown in this figure isequipped with a main control device 40A. The main control device 40Aincludes a load shift calculation unit (load shift calculation means)51, a road shoulder strength calculation unit (road shoulder strengthcalculation means) 54 and a load comparison judgment unit (loadcomparison judgment means) 52, in addition to the loaded weightestimation unit 32, the vehicle rotation moment calculation unit 33, theangle judgment unit 11 and the cylinder controller 39 explained above.

The load shift calculation unit 51 is connected with the vehiclerotation moment calculation unit 33. Based on the vehicle rotationmoment Mb calculated by the vehicle rotation moment calculation unit 33,the load shift calculation unit 51 calculates the load shift ΔFr of therear wheels 2 caused by the vehicle rotation moment Mb. The load shiftcalculation unit 51 in this embodiment calculates the load shift ΔFr ofthe rear wheels 2 by dividing the vehicle rotation moment Mb by thewheelbase Lw (ΔFr=Mb/Lw). The calculated load shift ΔFr is outputted tothe load comparison judgment unit 52 which is connected with the loadshift calculation unit 51.

The road shoulder strength calculation unit 54 is connected with theroad shoulder shape sensor 8. The road shoulder strength calculationunit 54 calculates the withstand load of the road shoulder where thevehicle is situated (road shoulder withstand load W) based on the roadshoulder shape data measured by the road shoulder shape sensor 8. Here,the road shoulder withstand load W represents the maximum value of aload applied to the road shoulder at which the road shoulder would notcollapse. The magnitude of the road shoulder withstand load W iscalculated by using an internal frictional angle φ (see FIG. 7)determined substantially by the type of the earth/sand forming the roadshoulder as will be explained below.

FIG. 7 is a side view schematically showing the idea of the roadshoulder strength calculation employed in the present invention. Theinternal frictional angle φ shown in this figure is an angle thatnaturally appears when the earth and sand crumble and defines a slidingplane 45. Collapse of the earth/sand 44 on the sliding plane 45 can beavoided if the magnitude of friction 42 caused by a vertical load 43 isgreater than a component of the resultant force of a load 46 by theearth/sand 44 and an axle load 41 by the vehicle's rear wheels 2 in thedirection of the sliding plane 45. Thus, the road shoulder withstandload W to be calculated is the magnitude of the axle load 41 where themagnitude of the component of the resultant force becomes equal to thefriction 42. Since the internal frictional angle φ is a value that isdetermined by the type of the earth/sand as mentioned above, the load 46by the earth/sand 44 can be calculated by using the angle of the slopeface part 21 and the distance from the rear wheels 2 to the slope facepart 21 which are acquired from the road shoulder shape data inputtedfrom the road shoulder shape sensor 8, and the road shoulder withstandload W can be calculated using the calculated load 46. The calculatedroad shoulder withstand load W is inputted to the load comparisonjudgment unit 52 connected to the road shoulder strength calculationunit 54.

The load comparison judgment unit 52 is a component for judging whetheror not a maximum rear axle load FR, which is calculated based on therear axle load Fr detected by the rear axle load sensor 31B and the loadshift ΔFr calculated by the load shift calculation unit 51, has exceededthe road shoulder withstand load W calculated by the road shoulderstrength calculation unit 54. The load comparison judgment unit 52 inthis embodiment determines the maximum rear axle load FR by adding theload shift ΔFr calculated by the load shift calculation unit 51 and therear axle load Fr measured by the rear axle load sensor 31B (FR=Fr+ΔFr),and judges the presence/absence of a margin of the road shoulderstrength by comparing the maximum rear axle load FR with the magnitudeof the road shoulder withstand load W calculated by the road shoulderstrength calculation unit 54. In short, the load comparison judgmentunit 52 judges the probability of an overturn of the vehicle by usingthe following expression (6).Fr+ΔFr>W  (6)When the expression (6) is judged to hold by the load comparisonjudgment unit 52, it is highly probable that the road shoulder collapsesand the vehicle overturns when the load 7 is discharged in a lump. Theload comparison judgment unit 52 thus transmits a signal to the displaydevice 37 to display information indicating that there is a strongprobability of a vehicle overturn. Similarly to the first embodiment,the load comparison judgment unit 52 may also be configured to transmita signal for reducing the expansion speed of the hoist cylinders 5 orfor stopping the expansion of the hoist cylinders 5 to the cylindercontroller 39 in addition to or in place of the signal transmitted tothe display device 37.

Next, the operation of the dump vehicle overturn preventing deviceconfigured as above will be described below. FIG. 8 is a flow chartshowing the flow of a process for judging the probability of an overturnof the vehicle executed by the dump vehicle overturn preventing devicein accordance with the second embodiment of the present invention.

The process shown in FIG. 8 is started when the switch (unshown) fortilting the body 3 is operated in order to discharge the load 7. First,the main control device 40A inputs the load data and the road shouldershape data acquired by the axle load sensors 31A and 31B and the roadshoulder shape sensor 8 (sensor values) to the loaded weight estimationunit 32, the road shoulder strength calculation unit 54 and the loadcomparison judgment unit 52 (step 81).

Subsequently, the loaded weight estimation unit 32 estimates the loadedweight “m” from the load data acquired by the axle load sensors 31A and31B (step 82). The vehicle rotation moment calculation unit 33calculates the vehicle rotation moment Mb using the loaded weight “m”estimated by the loaded weight estimation unit 32 (step 83). Then, theload shift calculation unit 51 calculates the load shift ΔFr by dividingthe vehicle rotation moment Mb calculated by the vehicle rotation momentcalculation unit 33 by the wheelbase Lw of the vehicle (step 84).

Meanwhile, the road shoulder strength calculation unit 54 extracts theangle of the slope face part 21 and the distance from the rear wheels 2to the slope face part 21 from the road shoulder shape data acquired inthe step 81, and calculates the road shoulder withstand load W by usingthe extracted angle and distance, the internal frictional angle φ, etc.(step 85).

After the step 85 is finished, the load comparison judgment unit 52calculates the maximum rear axle load FR by adding the rear axle load Fracquired in the step 81 and the load shift ΔFr calculated in the step84, and compares the calculated maximum rear axle load FR with the roadshoulder withstand load W calculated in the step 85 (step 86). When themaximum rear axle load FR is equal to or lower than the road shoulderwithstand load W, the process returns to the step 81 and the subsequentsteps are repeated. In contrast, when the maximum rear axle load FR isgreater than the road shoulder withstand load W in the step 86, theinformation indicating a strong probability of a vehicle overturn isdisplayed on the display device 37 for the driver (step 87). Thereafter,the process from the step 81 is repeated. As above, according to thisembodiment, it is possible to present information that can prompt thedriver to make a rational situational judgment in regard to the risk ofan overturn of the vehicle.

Incidentally, this embodiment has been designed in consideration of thefollowing point: The site where a dump vehicle discharges its load is inmany cases situated at the edge of a vertical hole for dumping earth,sand, etc. (so-called “pit”) and the ground of the road shoulder may befragile in some cases. Especially when the site is a pit where theground is unpaved and no measures such as reinforcement have been takenfor the slope face of the road shoulder, the load acting on the roadshoulder via the rear wheels suddenly increases when the load slidesdown from the body in a lump as in the first embodiment. The risk of thevehicle to overturn by collapse of the road shoulder is therefore high.In this regard, the overturn preventing device described in PatentDocument 1 has no mechanism for dealing with a risk of such roadshoulder collapse. The device would operate only after the road shoulderhas started to collapse, for which the effect of the device is limited.Thus, the object of the invention pertinent to this embodiment is toprovide a dump vehicle overturn preventing device capable of preventingan overturn of a vehicle caused by the sliding down of the load from thebody in a lump.

For this purpose, in the dump vehicle overturn preventing device inaccordance with this embodiment, the road shoulder strength calculationunit 54 calculates the road shoulder withstand load W based on the roadshoulder shape data (the distance from the rear wheels 2 to the slopeface part 21, the angle of the slope face part 21, etc.) measured by theroad shoulder shape sensor 8. The load comparison judgment unit 52estimates rational road shoulder collapse risk condition based on acivil engineering basis by comparing the maximum rear axle load FR (thesum of the axle load Fr at the rear wheels 2 and the load shift ΔFrcaused by the tilt of the body) with the road shoulder withstand load W.If the risk is high, the load comparison judgment unit 52 notifies of astrong probability of a vehicle overturn via the display device 37.Thus, according to this embodiment, information is provided to thedriver such that the driver can make a comprehensive and rationalsituational judgment (regarding also the strength of the road surface),whereby overturning of the vehicle caused by the load sliding down fromthe body in a lump can be prevented.

In this embodiment as well, the opening/closing of the switch 36 mayalso be controlled depending on the tilt angle of the body 3 byoperating the angle judgment unit 11 as in the first embodiment. Withthis configuration, it becomes possible, similarly to the firstembodiment, to reduce unnecessary issuance of a warning and to notifythe driver of a warning only when the warning is highly necessary.Further, it is also possible to control the expansion speed of the hoistcylinders 5 by the cylinder controller 39 depending on the result of thejudgment by the load comparison judgment unit 52 as in the firstembodiment. With this configuration, it becomes possible, similarly tothe first embodiment, to automatically stabilize the chassis when theprobability of occurrence of a great rear axle load gets high.Overturning of the vehicle can thus be prevented with high reliability.

Furthermore, it is also possible to configure a dump vehicle overturnpreventing device having the features of both the first and secondembodiments, by adding the load shift calculation unit 51, the roadshoulder shape sensor 8, the road shoulder strength calculation unit 54and the load comparison judgment unit 52 to the dump vehicle inaccordance with the first embodiment. In this case, in addition to theeffects of the first embodiment, the risk of a vehicle overturn causedby collapse of the road shoulder can also be included in the subjects ofthe judgment, whereby overturning of the vehicle can be prevented stillmore effectively.

While the best mode for carrying out the present invention has beendescribed above, specific configurations of the present invention arenot to be restricted to the above particular illustrative embodiments.It should be understood that design changes, etc. not departing from thespirit and scope of the present invention are naturally included in thepresent invention.

DESCRIPTION OF REFERENCE CHARACTERS

-   2 rear wheel-   3 body-   5 hoist cylinder-   7 load-   8 road shoulder shape sensor-   11 angle judgment unit-   21 slope face part-   31A front axle load sensor-   31B rear axle load sensor-   32 loaded weight estimation unit-   33 vehicle rotation moment calculation unit-   34 reference moment calculation unit-   35 judgment unit-   37 display device-   38 potentiometer (angle sensor)-   39 cylinder controller-   40 main control device-   51 load shift calculation unit-   52 load comparison judgment unit-   54 road shoulder strength calculation unit-   m loaded weight-   Mb vehicle rotation moment-   MI overturn threshold moment-   Ms reference moment-   Fr rear axle load-   ΔFr rear axle load shift-   FR maximum rear axle load-   W road shoulder withstand load

The invention claimed is:
 1. An overturn preventing device for a dump vehicle equipped with a body rotatably supported on a frame, rear wheels, and hoist cylinders that expand and contract to rotate the body around a rotation axis aligned substantially parallel with a rear-wheel axle, the device comprising: loaded weight estimation means which estimates loaded weight on the body; vehicle rotation moment calculation means which calculates a vehicle rotation moment about the rotation axis caused by movement of a dump vehicle's load upon discharging of the load based on the loaded weight estimated by the loaded weight estimation means; reference moment calculation means which calculates a minimum value of a rotation moment required to lift front wheels of the vehicle off the ground and sets a reference moment not greater than the minimum value; judgment means which judges whether or not the vehicle rotation moment calculated by the vehicle rotation moment calculation means has exceeded the reference moment calculated by the reference moment calculation means; and notification means which notifies a driver that there is a probability of an overturn of the vehicle when the judgment means judges that the vehicle rotation moment has exceeded the reference moment.
 2. The overturn preventing device for a dump vehicle according to claim 1, further comprising: angle detecting means which detects a tilt angle of the body with respect to the frame; and angle judgment means which judges whether or not the detected value of the angle detecting means has exceeded a preset angle, the preset angle being a tilt angle of the body at which a vehicle rotation moment so as to cause the vehicle to overturn cannot occur; wherein the notification means makes the notification that there is a probability of an overturn of the vehicle only when the angle judgment means judges that the detected value of the angle detecting means has exceeded the preset angle.
 3. The overturn preventing device for a dump vehicle according to claim 1, further comprising cylinder control means which reduces expansion speed of the hoist cylinders or stops expansion of the hoist cylinders when the judgment means judges that the vehicle rotation moment has exceeded the reference moment.
 4. The overturn preventing device for a dump vehicle according to claim 1, further comprising: rear axle load detecting means which detects a load acting on the rear wheels of the vehicle; load shift calculation means which calculates a load shift of the rear wheels caused by the vehicle rotation moment based on the vehicle rotation moment, the vehicle rotation moment being calculated by the vehicle rotation moment calculation means; road shoulder shape measurement means which measures the distance from the vehicle to a road shoulder behind the vehicle and the shape of the road shoulder; road shoulder strength calculation means which calculates a withstand load of the road shoulder based on the road shoulder shape measured by the road shoulder shape measurement means; and load comparison judgment means which judges whether or not a maximum rear axle load, calculated based on the rear axle load detected by the rear axle load detecting means and the rear axle load shift calculated by the load shift calculation means, has exceeded the withstand load of the road shoulder calculated by the road shoulder strength calculation means; wherein the notification means notifies the driver that there is a probability of an overturn of the vehicle also when the load comparison judgment means judges that the maximum rear axle load has exceeded the withstand load of the road shoulder.
 5. An overturn preventing device for a dump vehicle equipped with a body rotatably supported on a frame, rear wheels, and hoist cylinders that expand and contract to rotate the body around its rotation axis aligned substantially parallel with a rear-wheel axle, the device comprising: front axle load detecting means which detects a load acting on a front wheels of the vehicle; rear axle load detecting means which detects a load acting on a rear wheels of the vehicle; loaded weight estimation means which estimates loaded weight on the body based on the detected values of the front axle load detecting means and the rear axle load detecting means; vehicle rotation moment calculation means which calculates a vehicle rotation moment about the rotation axis that is expected to occur when the dump vehicle's load slides down from the body in a lump based on the loaded weight estimated by the loaded weight estimation means; reference moment calculation means which calculates a minimum value of the rotation moment required to lift front wheels of the vehicle off the ground based on the detected values of the front axle load detecting means and the rear axle load detecting means and sets a reference moment not greater than the minimum value; judgment means which judges whether or not the vehicle rotation moment calculated by the vehicle rotation moment calculation means has exceeded the reference moment calculated by the reference moment calculation means; and notification means which notifies a driver that there is a probability of an overturn of the vehicle when the judgment means judges that the vehicle rotation moment has exceeded the reference moment. 